Problem: Simplify the following expression: $t = \dfrac{1}{3x} - \dfrac{1}{10x}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $3x$ and $10x$ $\lcm(3x, 10x) = 30x$ $ t = \dfrac{10}{10} \cdot \dfrac{1}{3x} - \dfrac{3}{3} \cdot \dfrac{1}{10x} $ $t = \dfrac{10}{30x} - \dfrac{3}{30x}$ $t = \dfrac{10 -3}{30x}$ $t = \dfrac{7}{30x}$